I'm finding that I need to prioritise a Tech advancement - I was hanging out to pull Ghost because I loved using her in the 5* days (even as an ascended 5* her damage is really starting to lack) but after 3 Tech Nexus crystals in a row failed to offer her up I need to focus elsewhere, but I'm a bit stumped for who to priotise because I don't really know how to use any of them and/or what specialty they offer that I'm lacking. I've tried watching some videos but having a hard time putting it into practice.

I've got no 7* Techs at all. I've got Warlock as my only R4, then a bunch of R3s whom I pretty much entirely took up due to Tier Lists etc, then a couple of older R2s and a bunch at R1.
For Context I'm Paragon, have done a Completion run of everything in Story including 8.3 and am working through exploring Act 8 in anticipation of 8.4 releasing - this rank-up could be useful for 8.3.5's Bishop boss. I've also done a single run of Necropolis but am not expecting to do it again any time soon so I'm counting on Act 8's exploration giving what I need to become Valiant. I mostly just do general content, low-pressure AW, but am looking to dip my toes back into Battlegrounds now that my roster's had a real shake-up.
What I would really appreciate, please, is not only recommendations for which of these champs I should be looking to prioritise, but also why and where they're most useful - like they're great for the Tech chapter in EQ, or they're amazing through Acts 7 and 8 to explore. I know Shuri is one of the champs for Necropolis, but is it worth investing all the resources into a 6* for that? I'm finding it all a bit of information overload now so getting some direct advice would be really helpful - thanks!